1. Field of the Invention
The present invention relates to an image forming apparatus equipped with a developing unit to make the developing and simultaneous cleaning for electro-photographic type copiers, printer and the like and an image forming method.
2. Description of the Related Art
In recent year, among image forming apparatus such as copying machines, printers, etc., there is an image forming apparatus adopting less cleaner type developing units without scraping toners remaining on photosensitive drums with a blade, etc. after transferring images and recover toners simultaneously with development in the subsequent image forming process. Such image forming apparatus prevents abrasion of photosensitive drums and is able to use toners by recycling.
However, in a cleaner-less type image forming apparatus, it tends to generate the state that toners always remain on the same portions of photosensitive drums. Therefore, when the image forming process is repeatedly conducted using this cleaner-less type image forming apparatus, a so-called filming phenomenon where toners remaining for a long time are firmly fixed on the surfaces of photosensitive drum is generated. When the filming phenomenon is generated, voids are produced on toner images and the image quality drops.
So, for example, in the Japanese Patent Application Publication No. 05-61383, an apparatus to prevent the filming by erasing image memories on the surfaces of photosensitive drums after completing the image transfer using vibrating or oscillating brushes is disclosed. Further, in the Japanese Patent Application Publication No. 2000-181309, an apparatus to prevent the filming by removing paper-dust on the surfaces of photosensitive drums after completing the transfer by rotating paper-dust removing rollers equipped with brushes is disclosed.
However, in the conventional apparatus described above, all of brushes are attached to mounting shafts and vibrate, oscillate or rotate centering around the attached shaft. On the other hand, for manufacturing accuracy or assembling accuracy of the photosensitive drums, it is difficult to hold the surface positions of the photosensitive drum constant and the surface positions are displaced. When the surface positions of the photosensitive drums are displaced, the filming preventive brushes are pushed and bent by such a surface position displacement, so that ends of the brushes are not in sufficient contact with the surfaces of the photosensitive drums but bent portions other than the ends of the brushes come into contact with them, which are hereinafter collectively called “bent-portion contacts” of the brushes. As a result, the brushing effect is reduced remarkably and the filming preventive effect is lowered.
So, in the field of image forming apparatus adopting a cleaner-less system, an image forming apparatus and an image forming method capable of getting the high-grade image quality by effectively erasing image memories remaining on photosensitive drums using brushes and surely preventing the filming phenomenon after transferring images are demanded.